Baucus is the first top Democrat to publicly voice fears about the rollout of the new health care law, designed to bring coverage to 30 million uninsured people through a mix of government programs and tax credits for private insurance.

Polls show that Americans remain confused by the complex law, and even many uninsured people are skeptical that they will be helped by benefits that start next year.

Baucus, a six-term veteran, expects a tough re-election battle in 2014. He's still trying to recover from approval ratings that nose-dived amid displeasure with the health care law in his home state.

He said he's “very concerned” that new health insurance marketplaces for consumers and small businesses will not open on time in every state and that if they do, they might just flop because residents don't have the information they need to make choices.

“The administration's public information campaign on the benefits of the Affordable Care Act deserves a failing grade,” he told Sebelius. “You need to fix this.”

Responding to Baucus, Sebelius pointedly noted that Republicans in Congress last year blocked funding for carrying out the health care law and she had to resort to raiding other legally available departmental funds.

The administration is asking for $1.5 billion in next year's budget, and Republicans don't seem willing to grant that, either.

At one point, as Sebelius tried to answer Baucus' demand for facts and figures, the senator admonished: “You haven't given me any data; you just give me concepts, frankly.”

“I don't know what he's looking at,” Sebelius told reporters following her out of the room after Baucus adjourned the hearing. “But we are on track to fully implement marketplaces in Jan. 2014, and to be open for open enrollment.”

That open enrollment launch is only months away, Oct. 1. It's when millions of middle-class consumers who don't get coverage through their jobs can start shopping for a private plan in the new marketplaces. They'll also be able to find out if they qualify for tax credits that will lower their premiums.

At the same time, low-income people will be steered to government programs, mainly an expanded version of Medicaid.

Half the states, most of them Republican-led, have refused to set up the infrastructure of Obama's law.

The overhaul law provided that the federal government would step in and run the new markets if a state failed to do so.

Envisioned as a fallback, federal control now looks like it will be the norm in much of the country, straining resources.

After the hearing, Baucus' office clarified that he still thinks the Affordable Care Act is a good law, but he questions how it is being carried out.